Convert end-to-end tests to use bash_unit

What does this MR do?

Converts end to end tests to use bash_unit. This should make our tests easier to read, more modular, and faster as there used to be a lot of duplication in the previous style tests. We have also had issues as the end-to-end job has been broken for sometime without us realising.

We have spoken about moving these tests to Python in future, however with the requirement of using Docker in the tests this was a fast and effective approach.

Note that we should fix/merge !56 (merged) before merging this MR.